American Society of Heating, Refrigerating and Air-conditioning Engineers Guideline 12-2000: Minimizing the Risk of Legionellosis Associated with Building Water Systems

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE's) Environmental Health Committee recognized the need for a comprehensive, nationally accepted guideline to address the public health issues surrounding Legionnaires' disease. The primary focus is on control and prevention of contaminated water sources, but it is limited to discussion of cooling towers and domestic water systems. Guideline Project Committee (GPC)-12 was composed of members with diverse backgrounds ranging from physicians to consulting engineers and microbiologists to manufacturers. Investigation of Legionnaires' disease outbreaks suggested that, in most instances, transmission to humans occurred when water containing the organism was aerosolized into droplets less than 5 μm in diameter, allowing inhalation into the lungs of a susceptible host. Conventional open cooling towers are evaporative heat-transfer devices in which atmospheric air mixes with and cools warm water by evaporating a portion of the water. Heated spas generally operate in the temperature range of 32 to 40№ C, which is in the range that favors amplification. ASHRAE Guideline 12 presents information on several budding water systems that can amplify and disseminate Legionella. This chapter thus focuses on three of these amplifiers: cooling towers, evaporative condensers, and heated spas. Specific guidance is presented to minimize the risk of legionellosis associated with these devices.